Apparatus clutch controlled closure means for a molding

ABSTRACT

A molding machine which performs molding by means of one mold part held by a fixed platen and the other mold part held by a movable platen movable toward and away from the one mold part. A shaft having an axis extending in the direction of reciprocal movement of the movable platen is disposed on a stationary frame for rotation with respect thereto and for reciprocal movement along the axis of the shaft, and is rotated by an electrical motor. First and second nut members are respectively screwed onto first and second threaded portions formed along the axis of the shaft. The first nut member is secured to one of the stationary frame and the movable platen while the second nut member is capable of being rigidly coupled with the other thereof via a clutch. While the shaft is being rotated, the second nut member is rigidly coupled with the other of the stationary frame and the movable platen via the clutch, a relative movement is produced between the shaft and the first and second nut members. Also, when the second nut member is released from rigid coupling with respect to the other of the stationary frame and the movable platen via the clutch, a relative movement is produced between the shaft and the first nut member, but, since the second nut member is rotated together with the shaft, no relative movement is produced therebetween.

BACKGROUND ART

The present invention relates to a molding machine which is arranged toperform molding with the use of at least one mold constituted by a pairof mold parts, and more particular to a mold clamping apparatus for usewith an injection molding machine employing an electrical motor.

TECHNICAL FIELD

Japanese Patent Unexamined Publication No. 125619/1985 discloses a moldclamping apparatus for use with an injection molding machine of the typewhich has a fixed platen holding one of a pair of mold parts. The moldclamping apparatus has a shaft rotatably supported by a stationaryframe. One end of the shaft is drivably coupled with an electrical motorand the portion of the shaft adjacent to the end has a first threadedportion while the portion of the same adjacent to the other end has asecond threaded portion with a lead smaller than that of the firstthreaded portion. First and second nut members are respectively screwedonto the first and second threaded portions, the first and second nutmembers capable of being rigidly coupled with a rod via first and secondclutches, respectively. The rod is rigidly coupled with a movable platenwhich holds the other of the aforesaid pair of mold parts and which isdisposed for reciprocal movement toward and away from the aforesaid oneof the same pair. The first clutch is capable of traveling between anengagement position which allows the first nut member to be moved alongthe shaft during rotation of the shaft with the first nut member rigidlycoupled with the rod and a disengagement position which allows the firstnut member to be moved along with the shaft during rotation of the shaftwith the first nut member released from such rigid coupling with respectto the rod. The second clutch is likewise capable of traveling betweenan engagement position which allows the second nut member to be movedalong the shaft during rotation of the shaft with the second nut memberrigidly coupled with the rod and a disengagement position which allowsthe second nut member to be moved along with the shaft during rotationof the shaft with the second nut member released from such rigidcoupling with respect to the rod.

Mold closing is performed as follows. The first clutch is placed in itsengagement position while the second clutch is placed in itsdisengagement position. When the shaft is rotated, the movable platenwhich holds the one of the pair of mold parts is moved toward the othermold part at a relatively high feed rate in cooperation between thefirst threaded portion having a relatively large lead and the first nutmember screwed onto the same. The mold part held by the movable platenand the mold part held by the fixed platen are combined with each other,thereby completing the mold closing step.

Upon completion of mold closing, the first clutch is placed in itsdisengagement position while the second clutch is placed in itsengagement position. When the shaft is rotated, the other mold part isforced against the one at a relative slow speed, that is, with arelatively large mold clamping force, in cooperation between the secondthreaded portion with a relatively small lead and the second nut memberscrewed thereonto.

The above-described mold clamping apparatus of the prior art hasadvantage in that the opening and closing of the mold at a relativelyhigh feed rate and mold clamping with a large mold clamping force can beperformed by means of an electrical motor with a relatively smallcapacity and in that the molding cycle can be reduced. However, wheneither of the first and second nut members is rigidly coupled with therod, the other thereof is necessarily released from rigid coupling withrespect to the rod. It is therefore necessary to form the first andsecond threaded portions along the axis of the shaft over a relativelylong range thereof. Accordingly, the shaft must be lengthened and thismay result in the disadvantage that the overall size of the moldingmachine increases.

It is therefore an object of the present invention to provide a moldingmachine which possesses the advantage of the prior art and yet theoverall size of which can be reduced.

DISCLOSURE OF INVENTION

The present invention provides a molding machine which is arranged toperform molding by means of at least one mold constituted by a pair ofmold parts, comprising:

a stationary frame;

a fixed platen holding one of the pair of mold parts;

a movable platen holding the other of the pair of mold parts, themovable platen being attached to the stationary frame for reciprocalmovement with respect to the fixed platen in the direction toward andaway from the one of the pair of mold parts;

a shaft having an axis extending toward the movable platen, the shaftbeing supported for rotation with respect to the stationary frame andfor reciprocal movement along the axis of the shaft, the shaft havingfirst and second threaded portions formed thereon along the axis of theshaft;

an electrical motor mounted on the stationary frame for causing rotationof the shaft;

first and second nut members screwed onto the respective first andsecond threaded portions of the shaft, the first nut member beingsecured to one of the stationary frame and the movable platen, the firstnut member and the shaft being movable with respect to each other whenthe shaft is rotated, the second nut member capable of being rigidlycoupled with the other of the stationary frame and the movable platen;and

clutch means disposed between the other of the stationary frame and themovable platen and the second nut member for free movement between anengagement position which allows for relative movement between the shaftand the second nut number while the shaft is being rotated with thesecond nut member rigidly coupled with the other of the stationary frameand the movable platen and a disengagement position which allows theshaft to be rotated together with the second nut member while the shaftis being rotated with the second nut member released from rigid couplingwith respect to the other of the stationary frame and the movableplaten.

Accordingly, the molding machine of the present invention is arranged insuch a manner that the first and second threaded portions are both usedfor the purpose of opening and closing the mold, only the first threadedportion being utilized to move the one of the mold parts With respect tothe other for the purpose of mold clamping. Alternately, only the secondthreaded portion is utilized for the purposes of opening and closing themold while, for mold clamping, the first and second threaded portionsare both utilized to move the one of the mold parts with respect to theother Accordingly, the opening and closing of a mold at high speed andmold clamping with a large mold clamping force can be performed by meansof an electric motor with a relatively small capacity. In addition, theoverall length of the shaft can be reduced, and hence, the overall sizeof the molding machine can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partly sectional view of a first preferred embodiment of amolding machine in accordance with the present invention, showing astate wherein a movable platen holding a mold part is placed at aposition where a mold is opened;

FIG. 2 is a partly sectional view of the first embodiment but showing astate wherein the movable platen shown in FIG. 1 is placed at a positionwhere the mold is closed;

FIG. 3 is a view similar to FIG. 1 but showing a second preferredembodiment of the present invention; and

FIG. 4 is a view similar to FIG. 1 but showing a third preferredembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to the accompanying drawings.

FIG. 1 partly shows the first preferred embodiment of an injectionmolding machine in accordance with the present invention. The injectionmolding machine includes: a fixed platen 10 holding a mold part 11 whichconstitutes one of a pair of mold parts; and a stationary frame 12coupled with the fixed platen 10 via tie bars 13 and 14. A movableplaten 15 holding a mold part 16 which constitutes the other of the pairof mold parts is fitted onto the tie bars 13 and 14 for reciprocalmovement therealong.

A shaft 20 has an axis which extends in the direction in which themovable platen 15 is moved reciprocally along the tie bars 13 and 14,and is supported for rotation with respect to the stationary frame 12and for reciprocal movement along the axis of the shaft 20. The shaft 20is provided with two threaded portions 21 and 22 which are formed alongthe axis. The threaded portion 21 has a thread which spiral in theopposite directions to the thread of the other threaded portion 22, andhas a lead smaller than the lead of the portion 22.

A nut member 25 is screwed onto the threaded portion 21 via a pluralityof balls 24, and is rigidly attached to the stationary frame 12. Also, anut member 26 is screwed onto the threaded portion 22 via a plurality ofballs 27. The nut member 26 is rigidly attached to a housing 28, and thehousing 28 is rotatably supported via a bearing 31 on a cylindricalprojection 29 which is coaxial and integral with the movable platen 15.

A first sliding clutch mechanism 30 is disposed between the housing 28and the shaft 20, the first sliding clutch mechanism 30 beingconstituted by a clutch component 32 secured to a radially inward flange33 which is integral with the housing 28 and a clutch component 34secured to a radially outward flange 36 which is integral with the shaft20. The first sliding clutch mechanism 30 is arranged for movementbetween the disengagement position shown in FIG. 1 and the engagementposition shown in FIG. 2.

A second sliding clutch mechanism 40 is disposed between the movableplaten 15 and the housing 28, the second sliding clutch mechanism 40being constituted by: an annular clutch component 41 made of a magneticmaterial which is disposed on a radially outward flange 42 integral withthe housing 28; an annular clutch component 43 secured to thecylindrical projection 29 of the movable platen 15; and a solenoid 44incorporated in this clutch component 43. The clutch component 41 issupported on the housing 28 for movement along the axis of the shaft 20but for nonrotation with respect to the housing 28, and is pressed by aspring (not shown) in the direction away from the clutch component 43.While the solenoid 44 is being de-energized, the clutch component 41 isheld away from the clutch component 43 by means of the spring (notshown) and the second sliding clutch mechanism 40 takes thedisengagement position shown in FIGS. 1 and 2. When the solenoid 44 isenergized, the clutch component 41 is attracted by the solenoid 44against the force of the spring and comes into contact with the clutchcomponent 43. Thus, the second sliding clutch mechanism 40 takes anengagement position (not shown).

The shaft 20 has a male spline 51 at one end thereof on the sideopposite to the movable platen 15, and the male spline 51 is meshed Witha female spline 52 formed on a rotary member 53. The rotary member 53 isrotatably supported on the stationary frame 12 via a bearing 54. Also, apulley 56 is secured to the rotary member 53, and the pulley 56 iscoupled via a belt 58 with an output shaft 59 of an electrical motor 60secured to the stationary frame 12.

The operation of the injection molding machine having theabove-described construction will be described below. FIG. 1 shows amold open state wherein the mold part 16 held by the movable platen 15is positioned away from the mold part 11 held by the fixed platen 10. Insuch a state, an electrical signal representing the commence of moldclosing is supplied to the electrical motor 60 to cause rotation of theoutput shaft 59. Simultaneously, the second sliding clutch mechanism 40is moved to its engagement position, and the clutch component 41 isthereby caused to engage with the clutch component 43 to bring thehousing 28 into a non-rotatable state with respect to the movable platen15. Thus, the nut member 26 is rigidly coupled with the movable platen15. As the consequence, the rotation of the aforesaid motor 60 istransmitted via the belt 58 to the pulley 56 and the rotating member 53,so that the shaft 20 is rotated counterclockwise as viewed in themold-closing direction in which the mold part 16 approaches the moldpart 11 held by the fixed platen 10, that is, in the direction indicatedby an arrow 61 in each of FIGS. 1 and 2. When the shaft 20 is rotated,the shaft 20 is moved along its axis in the mold-closing direction bythe cooperation between the threaded portion 21 formed on the shaft 20and the nut member 25 which is secured to the stationary frame 12 andmeshed with the portion 21. Also, the shaft 20 is forced to travelcounter to the mold closing direction by the cooperation between thethreaded portion 22 and the nut member 26 which is rigidly coupled withthe movable platen 15 via the second sliding clutch mechanism 40.Therefore, the movable platen 15 is moved along the tie bars 13 and 14in the direction in which the mold is closed, with the stationary frame12 serving as a reaction receiver. Therefore, the movable platen 15 ismoved at high speeds equivalent to the rotation of a hypothetical screwhaving a lead substantially equal to the sum of the leads of thethreaded portions 21 and 22, thereby performing a mold-closing step.

The first sliding clutch mechanism 30 is arranged such that it is placedat the engagement position shown in FIG. 2 immediately before the moldpart 16 held by the movable platen 15 comes into contact with the othermold part 11 held by the fixed platen 10 after the mold-closing step hasfurther proceeded. In addition, when a pair of the mold parts 11 and 16come into contact with each other, a detecting mechanism (not shown)supplies a signal to the second sliding clutch mechanism 40, therebyde-energizing the solenoid 44. The aforesaid arrangement allows thehousing 28 to rotate together with the shaft 20 with the clutchcomponent 41 of the second sliding clutch mechanism 40 brought intosliding contact with the clutch component 43 of the same immediatelybefore the mold closure. Upon completion of the mold closure, thearrangement also allows the housing 28 to rotate together with the shaft20 without the clutch component 41 of the second sliding clutchmechanism 40 brought into sliding contact with the clutch component 43of the same. Therefore, no relative movement occurs between the threadedportion 22 and the nut member 26 and thus the shaft 20 is caused totravel at a relatively low speed only by the cooperation between thethreaded portion 21 having a smaller lead and the corresponding nutmember 25. This produces a large mold clamping force, and themold-clamping step is performed by the large mold clamping force.

If the mold clamping is to be continued, the electrical motor 60 may bemaintained in the state of generating a torque, or a motor with a brakemay be employed so as to hold the mold clamping force via the brakemechanism.

Mold opening is performed in the following manner. The electrical motor60 is reversed with the second sliding clutch mechanism 40 maintained inits engagement position, and the first sliding clutch mechanism 30 isdisengaged. As in the case of the mold closing, the shaft 20 is made totravel at high speed in the direction counter to that of mold closure bythe cooperation between the threaded portion 21 and the nut member 25 aswell as by the cooperation between the threaded portion 22 and the nutmember 26. Thus, the mold opening step is performed.

It is to be noted that, in order to obtain a large mold-clamping forcein the aforesaid mold-closing step, it is necessary that the mold parts11 and 16 come into contact with each other after the first slidingclutch mechanism 30 has been placed in its engagement position.Therefore, when an old mold is to be replaced with a new mold, thesecond sliding clutch mechanism 40 is placed in its engagement position,prior to the mounting of the new mold, the electrical motor 60 beingactivated to move the movable platen 15, thereby engaging the clutchmechanism 30. Subsequently, the clutch mechanism 40 is disengaged andthe aforesaid motor 60 is reversed, thereby moving the movable platen 15backwards. Thus, the interval between the fixed platen 10 and themovable platen 15 is adjusted so that the interval may be made slightlywider than the thickness of the new mold.

As described above, in the first preferred embodiment of the presentinvention, the opening and closing of a mold can be performed at highspeed with simultaneous use of the two threaded portions whoserespective thread directions are opposite to each other. In addition,rigid mold clamping can be performed with the use of either of thethreaded portions. Accordingly, the operation of the injection moldingmachine can be performed effectively and positively by means of anelectrical motor having a small capacity, this being favorable forhigh-cycle molding and in terms of the cost and electrical capacity.Moreover, since the overall length of the shaft is made shorter thanthat of the prior art, the overall size of the injection molding machinecan be reduced.

FIG. 3 partly shows a second preferred embodiment of the injectionmolding of the present invention. In FIG. 3, like reference numerals areused to denote the like or corresponding components and parts that areshown in FIGS. 1 and 2. Detailed description of the invention istherefore omitted with respect to such like or corresponding componentsand parts.

A shaft 120 used in the second embodiment shown in FIG. 3 is providedwith threaded portions 121 and 122 having threads which spiral in theopposite directions to each other, the former having a lead which issmaller than that of the latter.

A nut member 125 is screwed onto the threaded portion 121 via aplurality of balls 124, and the nut member 125 is secured to thecylindrical projection 29 of the movable platen 15. Also, a nut member126 is screwed onto the threaded portion 122 via a plurality of balls127, the nut member 126 being secured to a tubular housing 128. Thehousing 128 is, in turn, rotatably supported via a bearing 131 on thestationary frame 12.

A first sliding clutch mechanism 130 is provided between the housing 128and the stationary frame 12. The first sliding clutch mechanism 130includes: a clutch component 132 formed by an outward flange integralwith the housing 128; a bracket 164 secured to the stationary frame 12;and a clutch component 133 supported for movement along the axis of theshaft 120. The first sliding clutch mechanism 130 is arranged to takethe disengagement position shown in FIG. 3 in which the clutch component133 is separated from the clutch component 132 and to take an engagementposition (not shown) in which the clutch component 133 is maintained infrictional engagement with the clutch component 132.

A second sliding clutch mechanism 140 is provided between the housing128 and the rotary member 53. The second sliding clutch mechanism 140includes: a clutch component 141 made of a magnetic material which isdisposed on an outward flange member 142 secured to the housing 128; aclutch component 143 secured to an outward flange 163 integral with therotary member 53; and a solenoid 144 secured to the stationary frame 12.The clutch component 141 is supported on the housing 128 for movementalong the axis of the shaft 120 but for non-rotation with respect to thehousing 128, and is pressed by a spring (not shown) in the directionaway from the clutch component 143. While the solenoid 144 is beingde-energized, the clutch component 141 is held away from the clutchcomponent 143 by means of the spring (not shown) and the second slidingclutch mechanism 140 takes the disengagement position shown in FIG. 3.When the solenoid 144 is energized, the clutch component 141 isattracted to the solenoid 144 against the force of the spring and comesinto contact with the clutch component 143. Thus, the second slidingclutch mechanism 140 takes an engagement position (not shown).

The operation of the second embodiment shown in FIG. 3 will be describedbelow. In a state wherein the mold is opened as shown in FIG. 3, anelectrical signal indicative of the commencement of mold closing is fedto the electrical motor 60 to rotate the output shaft 59 and at the sametime to cause the first sliding clutch mechanism 130 to move toward itsengagement position, thereby rigidly coupling the housing 128 and thenut member 126 with respect to the stationary frame 12. Thus, therotational output of the motor 60 is transmitted to the pulley 56 andthe rotary member 53 via the belt 58, causing the shaft 120 to rotate inthe direction indicated at 161 in FIG. 3. In this way, as in the case ofthe first embodiment described in connection with FIGS. 1 and 2, themovable platen 15 is made to travel in the mold-closing direction athigh speed equivalent to the rotation of a hypothetical screw having alead substantially equal to the sum of the respective leads of thethreaded portions 121 and 122, whereby the mold closing step isperformed.

At the final stage of mold closing, detecting means such as acontactless switch is operated to detect the fact that the mold part 16held by the movable platen 15 and the mold part 11 held by the fixedplaten 10 approach each other. In response to the thus-detected signal,the first sliding clutch mechanism 130 is caused to move to itsdisengagement position and at the same time the second sliding clutchmechanism 140 is caused to move to its engagement position. Thus, therotational output of the motor 60 is transmitted to the housing 128 aswell, so that the housing 128 is rotated together with the shaft 120. Asin the case of the aforesaid first embodiment, a large mold clampingforce is produced only by the cooperation between the threaded portion121 having a smaller lead and the nut member 125, and thus the moldclamping step is performed by the large mold clamping force.

The mold clamping may be continued as in the case of the aforesaid firstembodiment.

Mold opening is performed in the following manner. After the electricalmotor 60 has been reversed to remove the mold clamping force, the firstsliding clutch mechanism 130 is moved to its engagement position and thesecond sliding clutch mechanism 140 is moved to its disengagementposition. The electrical motor 60 is further reversed, therebyperforming the mold opening at high speed as in the case of the moldclosing.

The above-described second embodiment provides substantially the sameeffect as that of the first embodiment.

FIG. 4 partly shows a third embodiment of an injection molding machinein accordance with the present invention. In FIG. 4, like referencenumerals are used to denote the like or corresponding components andparts that are shown in FIG. 3. Detailed descriptions are thereforeomitted with respect to such like or corresponding components and parts.

A shaft 220 used in the third embodiment shown in FIG. 4 is providedwith threaded portions 221 and 222 having threads which spiral in thesame directions as each other, the former having a lead which is largerthan that of the latter.

A nut member 225 is screwed onto the threaded portion 221 via aplurality of balls 224, and the nut member 225 is secured to thecylindrical projection 29 of the movable platen 15. Also, a nut member226 is screwed onto the threaded portion 222 via a plurality of balls27, the nut member 226 being secured to the housing 128 which issupported as in the case of the second embodiment shown in FIG. 3.

Also, as in the case of the second embodiment shown in FIG. 3, the firstsliding clutch mechanism 130 is provided between the housing 128 and thestationary frame 12 while the second sliding clutch mechanism 140 isprovided between the housing 128 and the rotary member 53.

The other construction of the third embodiment shown in FIG. 4 is thesame as that used in the second embodiment. Therefore, detaildescription thereof is omitted.

The operation of the third embodiment shown in FIG. 4 is describedbelow. In a state wherein the mold is opened as shown in FIG. 4, anelectrical signal indicative of the commencement of mold closing issupplied to the electrical motor 60 to cause rotation of the outputshaft 59. The rotational output of the aforesaid motor 60 is transmittedvia the belt 58 to the pulley 56 and the rotary member 53, and thus theshaft 220 is rotated together with the rotary member 53 in the directionindicated by an arrow 261 shown in FIG. 4. Simultaneously with therotation of the output shaft of the motor 60, the second sliding clutchmechanism 140 is moved to its engagement position, thereby rigidlycoupling the rotary member 53 with the housing 128. In consequence, thehousing 128 is rotated together with the shaft 220. No relative movementoccurs between the threaded portion 222 and the nut member 226, but arelative movement is produced between the threaded portion 221 and thenut member 225. Therefore, the movable platen 15 is moved at high speedby the cooperation between the threaded portion 221 having a larger leadand the nut member 225 in the direction in which the mold is closed,with the stationary frame 12 serving as a reaction receiver, therebyperforming the mold-closing step. The speed at which the movable platen15 travels at this step is determined by a combination of the lead ofthe threaded portion 221 and the rotational speed of the shaft 220.

At the final stage of mold closing, detecting means such as acontactless switch is operated to detect the fact that the mold part 16held by the movable platen 15 and the mold part 11 held by the fixedplaten 10 approach each other. In response to the thus-detected signal,the second clutch mechanism 140 is caused to travel to its disengagementposition and at the same time the first sliding clutch mechanism 130 iscaused to travel to its engagement position, thereby rigidly couplingthe housing 128 with the stationary frame 12. Thus, the shaft 220 ismoved with respect to the nut member 226 in the direction counter tothat of mold closure by the cooperation between the threaded member 222having a smaller lead and the nut member 226 secured to the housing 128and at the same time the shaft 220 is forced to travel with respect tothe nut member 225 in the same direction by the cooperation between thethreaded portion 221 having a larger lead and the nut member 225 securedto the movable platen 15. Therefore, the movable platen 15 is moved inthe direction in which the mold is closed and at a low speed equivalentto the rotation of a hypothetical screw having a lead substantiallyequal to the subtraction of the lead of the threaded portion 222 fromthat of the threaded portion 221. In consequence, mold clamping force isproduced, and the mold clamping step is performed by means of the moldclamping force.

The mold clamping force is as follows: ##EQU1## where F(kgf) representsthe mold clamping force, A₃ (mm) representing the lead of the threadedportion 221, A₂ (mm) representing the lead of the threaded portion 222,T(kg-m) representing the torque of the shaft 220 and the conversionefficiencies from the torque of the respective nut members 221 and 222to the axial motion of the shaft 220 being 100%.

As will be understood from the aforesaid equation, if the value of A₃-A₂ is reduced, a large mold clamping force can be obtained by a smalltorque. Accordingly, although the third embodiment shown in FIG. 4 is anexample in which the single shaft 220 is driven by the single electricalmotor 60 incorporated in a single injection molding machine, the thirdembodiment is also effective in driving the shafts of a plurality ofinjection molding machines by means of the common electrical motor 60.

The mold clamping may be continued as in the case of the firstembodiment.

The mold opening is performed as follows. After the electrical motor 60has been reversed to remove the mold clamping force, the first slidingclutch mechanism 130 is located at its disengagement position while thesecond sliding clutch mechanism 140 is moved to its engagement position.In addition, the electrical motor 60 is reversed, thereby performing themold opening at high speed as in the case of mold closing.

In the third embodiment of the present invention shown in FIG. 4, theopening and closing of the mold can be performed at high speed with theuse of either of the two threaded portions which spiral in the samedirections as each other. Use of both threaded portions enables rigidclamping of the mold, so that it is possible to achieve the same effectas that of the first embodiment.

Although the respective embodiments of the present invention have beendescribed above, the present invention is not confined solely to theparticular embodiments and various modifications can be employed. As anexample, although the first and the second embodiments show the twothreaded portions having different leads, they may have the same lead.Also, while reference is illustratively made to the structure in whichthe movable platen holding one of the mold parts is moved directly bythe electrical motor via the shaft, the invention is applicable to thecase where the cross head of a toggle type mold closing apparatus is tobe moved. Accordingly, the term "movable platen" used in the presentspecification should be construed as including the cross head. Inaddition, while it is illustratively stated that one of the mold partsis held by the fixed platen, it may be supported by a mold holdingmember disposed for reciprocal movement with respect to the fixedplaten.

Industrial Applicability

The present invention described above is applicable to a molding machineof any type which employs a pair of mold parts as in the case of aninjection molding machine and which is arranged to perform molding bymoving the pair of mold parts toward and away from each other.

What is claimed is:
 1. A molding machine which is arranged to performmolding by means of at least one mold constituted by a pair of moldparts, comprising:a stationary frame; a fixed platen holding one of saidpair of mold parts; a movable platen holding the other of said pair ofmold parts, said movable platen being attached to said stationary framefor reciprocal movement with respect to said fixed platen in a directiontoward and away from said one of said pair of mold parts; a shaft havingan axis extending toward said movable platen, said shaft being supportedfor rotation with respect to said stationary frame and for reciprocalmovement along said axis of said shaft, said shaft having first andsecond threaded portions formed thereon along said axis of said shaft;an electrical motor mounted on said stationary frame for causingrotation of said shaft; first and second nut members screwed onto saidrespective first and second threaded portions of said shaft, said firstnut member being secured to one of said stationary frame and saidmovable platen, said first nut member and said shaft being movable withrespect to each other when said shaft is rotated, said second nut membercapable of being rigidly coupled with the other of said stationary frameand said movable platen; and clutch means disposed between said other ofsaid stationary frame and said movable platen and said second nut memberfor free movement between an engagement position which allows forrelative movement between said shaft and said second nut member whilesaid shaft is being rotated with said second nut member rigidly coupledwith said other of said stationary frame and said movable platen and adisengagement position which allows said shaft to be rotated togetherwith said second nut member while said shaft is being rotated with saidsecond nut member released from rigid coupling with respect to saidother of said stationary frame and said movable platen.
 2. A moldingmachine according to claim 1, wherein said first and second threadedportions spiral in opposite directions to each other, said first nutmember being secured to said stationary frame and said clutch meansincluding a first sliding clutch mechanism disposed between said secondnut member and said shaft and a second sliding clutch mechanism disposedbetween said second nut member and said movable platen.
 3. A moldingmachine according to claim 2, wherein said first threaded portion has alead smaller than that of said second threaded portion.
 4. A moldingmachine according to claim 1, wherein said first and second threadedportions spiral in opposite directions to each other, said first nutmember being secured to said movable platen and said clutch meansincluding a first sliding clutch mechanism disposed between said secondnut member and said shaft and a second sliding clutch mechanism disposedbetween said second nut member and said stationary frame.
 5. A moldingmachine according to claim 4, wherein said first threaded portion has alead smaller than that of said second threaded portion.
 6. A moldingmachine according to claim 1, wherein said first and second threadedportions spiral in identical direction, said first nut member beingsecured to said movable platen and said clutch means including a firstsliding clutch mechanism disposed between said second nut member andsaid shaft and a second sliding clutch mechanism disposed between saidsecond nut member and said stationary frame.
 7. A molding machineaccording to claim 6, wherein said first threaded portion has a leadlarger than that of said second threaded portion.